1. Field of the Invention
The present invention relates to a novel terpolymer useful for inhibiting the formation of scale in water systems. More specifically, the terpolymer comprises monomers of acrylic or methacrylic acid, vinyl acetate and/or vinyl alcohol formed by hydrolysis of vinyl acetate, and sodium-1-allyloxy-2-hydroxypropyl sulfonate. These novel terpolymers are particularly effective in inhibiting the formation of inorganic scales derived from sparingly soluble salts of calcium, barium, magnesium, and the like. 2. Technology Description
Many industrial applications and residential areas utilize water containing relatively high concentrations of inorganic salts. These salts are formed by the reaction of metal cations, such as calcium, magnesium, or barium, with inorganic anions such as phosphate, carbonate and sulfate. These salts have low solubilities in water and as their concentration in solution increases, or as the pH or temperature of the water containing them increases, these salts tend to precipitate from solution, crystallize and form hard deposits or scale on surfaces. Scale formation is a problem in heat transfer devices, boilers, secondary oil recovery wells and on clothes washed with such hard waters.
Many cooling water systems, including industrial cooling towers and heat exchangers made from carbon steel experience corrosion problems caused by the presence of dissolved oxygen. Corrosion is combated by the addition of various inhibitors such as orthophosphate compounds and/or zinc compounds. The addition of phosphates, however, adds to the formation of highly insoluble phosphate salts such as calcium phosphate. Other inorganic particulates, such as mud, silt and clay, are commonly found in cooling water. These particulates tend to settle onto surfaces and thereby restrict water flow and heat transfer unless they are effectively dispersed.
The stabilization of aqueous systems containing scale forming salts and inorganic particulates involves one or a combination of mechanisms. Anti-precipitation involves the delay of precipitation by limiting the size of the salts to sub-colloidal dimensions possibly by adsorption of the inhibitor onto the salt crystal soon after nucleation, thereby interfering with further crystal growth. Dispersion of the precipitated salt crystals is another stabilization mechanism believed to be the result of the adsorption of the inhibitor onto precipitated crystals, thereby imparting an electronegative charge which retards agglomeration, settling and deposition on surfaces by repulsive forces. The adsorption of the inhibitor can also be used to stabilize the system by facilitating the dispersion and subsequent removal of other suspended particulates, such as mud silt and clay, and metals such as iron and zinc and their insoluble salts, from aqueous systems. Another stabilization mechanism involves the ability of the inhibitor to interfere with and distort the crystal structure of the scale making the scale more easily fracturable and dispersible.
A large number of compositions have been proposed for use as scale inhibitors. Most of these compositions comprise water soluble monomers and polymers. For example, U.S. Pat. No. 3,463,730 teaches the use of an acrylic acid/acrylamide copolymer useful as a scale inhibitor. U.S. Pat. Nos. 3,709,815; 3,928,196 and 4,552,665 and WO 83/02607 suggest that a copolymer including monomer units of 2-acrylamido-2-substituted propane-1-sulfonic acid or acid salts (abbreviated "AMPS") be used as a scale inhibitor. The references suggest that in a preferred embodiment, AMPS be copolymerized with ethylenically unsaturated momoners such as acrylic acid or methacrylic acid.
U.S. Pat. No. 3,806,367 further suggests that AMPS be used as a comonomer in a polymeric composition used to inhibit the formation of scales. Examples of comonomers suggested in the patent include acrylic and methacrylic acids, acid salts and esters; substituted and nonsubstituted acrylamides; vinyl compounds and esters; and the like. The reference also suggests that a terpolymer using AMPS and two of the monomers selected from the above listing be employed. WO 83/02607 suggests that the copolymers may contain minor amounts of (up to 5 mole percent) other monomeric units which are substantially inert with respect to the production of the copolymers. Suggested units are lower esters of acrylic or methacrylic acid, acrylonitrile and the like.
U.S. Pat. No. 4,469,615 teaches a water treating composition including a copolymer which is an addition reaction product of a glycidyl ether or glycidyl ester and an .alpha.,.beta.-ethylenically unsaturated carboxylic acid and another vinyl monomer other than the addition reaction product monomer.
U.S. Pat. No. 4,566,973 teaches the use of a copolymer of acrylic acid with a substituted acrylamide to inhibit the formation of phosphate scale in water systems. Preferred acrylamides suggested include diacetoneacrylamide, N-t-butylacrylamide and N,N-dimethylacrylamide.
U.S. Pat. No. 4,532,048 suggests the use of a terpolymer in method for inhibiting scale formation. The terpolymer includes monomer units of (i) acrylic or methacrylic acid; (ii) a lower alkenyl carboxylate; and (iii) a salt of a lower alkenyl sulfonate. A preferred terpolymer includes monomers of acrylic acid, vinyl acetate and sodium vinyl sulfonate. The terpolymer is claimed to be particularly effective against calcium phosphate, zinc phosphate and magnesium phosphate. U.S. Pat. No. 4,604,211 also suggests that this preferred terpolymer be used as a dispersant for industrial water systems.
A series of patents assigned to Betz Laboratories of Trevose, Pa., teach the use of a specific polymer for water treatment. These include U.S. Pat. Nos. 4,560,481; 4,659,481; 4,659,482; 4,671,880; 4,717,499; 4,732,698; 4,931,188; and 4,944,885. The polymer includes monomeric units of, preferably, acrylic or methacrylic acid, an ester thereof or an amide thereof along with an allyl ether monomer containing a metal salt. The preferred allyl ether monomer described is 1-propane sulfonic acid, 2-hydroxy-3-(2-propenyloxy)-mono sodium salt (therein called "AHPSE"). U.S. Pat. Nos. 4,659,481; 4,659,482; 4,717,499; 4,732,698; and 4,944,885 suggest that AHPSE monomers may be incorporated into a water soluble terpolymer backbone having other repeat units including acrylic acid monomers, alkyl acrylate monomers, methacrylic acid monomers and acrylamide monomers. Despite this suggestion, no examples of such terpolymers are enabled in the patents. U.S. Pat. No. 4,931,188 suggests that a terpolymer be formed using the above mentioned monomers along with an additional monomer such as ethylene, styrene or alkylvinyl phosphonic acid. Despite this suggestion, no examples of such terpolymers are enabled in the patent.
A discussion of the results obtained when using an acrylic acid/AHPSE copolymer is presented in the article entitled "A Newly Developed Polymer to Inhibit Scale in Cooling Water Systems", authored by Imai and Uchida (Materials Performance, May 1989, pp. 41-44).
U.S. Pat. No. 4,500,693 discloses copolymers useful as scale inhibitors and pigment dispersants. The copolymer is made up of monomeric units including 50 to 99.5 mol percent of at least one (meth)acrylic acid-based monomer and 0.5 to 50 mol percent of at least one allyl ether-based monomer. One such set of monomers disclosed is 3-allyloxy-2-hydroxypropane-1-sulfonic acid and alkali metal salts thereof.
EPO 0 271 035 discloses the treatment of aqueous systems by using a polymer including at least one of each of the following monomers: (a) a monounsaturated carboxylic acid, including salts and anhydrides thereof, the acid having 3 to 5 carbon atoms; (b) an acrylamidoalkane sulfonic acid and salts thereof, such as AMPS; and (c) a primary copolymerizable monomer selected from one of a number of groups. One such group of monomers disclosed for monomer (c) is allyloxy hydroxyalkane sulfonic acids and salts thereof. Despite this disclosure, no examples utilizing these monomers is presented.
U.S. Pat. No. 4,711,725 discloses a terpolymer or interpolymer useful for treating aqueous systems. The compositions are derived from at least the following three types of monomers: (a) (meth)acrylic acids and salts; (b) acrylamido alkyl or aryl sulfonates; and (c) at least one unit derived form certain vinyl esters, vinyl acetates and substituted acrylamides. The most preferred terpolymer of these compounds includes 57% by weight (meth)acrylic acid or salt units, 23% by weight AMPS and 20% by weight of a vinyl ester, vinyl acetate or alkyl substituted acrylamide.
U.S. Pat. No. 4,963,267 discloses compositions useful for reducing and stabilizing manganese deposits. The compositions are water-soluble polymers having a pendant functionality including an amide linkage. The patent further suggests that these amide-linkage containing polymers can be copolymerized with units which are preferably substantially carboxylate-containing units and unsubstituted pendant amide-containing units. In still another use, the polymers can be used in combination with acrylamide units and acrylic acid units to form a terpolymer.
Despite these above compositions, there still exists a need for compositions which are cost effective to produce and can function as superior antiscalants against several types of inorganic scales such as calcium carbonate, calcium sulfate, calcium phosphate, barium sulfate, magnesium scales and the like.